This is an update from the joint hearings by the Coast Guard and the Bureau of Ocean Energy Management, Regulation and Enforcement investigating the causes of the Deepwater Horizon oil rig explosion on April 20.

Winslow is just the latest eyewitness to describe a certain amount of concern with the results of a critical test that afternoon called a "negative pressure test."

The test, which is supposed to measure the strength of the well structure when pressure is exerted upon it, has been a major point of contention in the investigation of what went wrong.

"It appeared there was some confusion about pressures or volumes circulated around that time and I heard the word negative test," Winslow said. "I thought it was not a good environment to have a tour group there."

At that point, Winslow asked the top Transocean official on the rig, Jimmy Harrell, and Miles Ezell, the senior toolpusher, to break away from the tour group and stay with the drill team.

Later, Winslow said Harrell told him everything was OK on the drill floor.

Rig and shore-side officials interpreted the test results to mean it was safe to proceed in removing heavy drilling mud that is meant, in part, to keep oil and gas from bulging up out of the well during operations.

That decision meant there was little mud left to counterbalance the gas that shot to the surface and set the rig on fire.

The first time the test was run, 15 barrels of drilling fluid escaped from the well. A well with good integrity will hold all of its contents and nothing should escape. So, the rig crew decided to run the test again, with more pressure on a valve in the blowout preventer mechanism to close off the top of the hole. That time, witnesses and documents say, there were worrisome increases in pressure on a drill pipe, but no fluid was lost.

There are conflicting reports as to how this was determined to be a good result. Winslow, who has 34 years of experience, testified that a successful test should show no increase in pressure on the drill pipe.

"If individuals recognize abnormal pressure, you stop the job and regroup," he said. "Whatever you do, you don't continue forward until you understand that."

Winslow testified Tuesday that "the customer," in this case BP, would have made the decision that the test was a success. But Harrell, a Transocean employee, testified at hearings in June in Kenner that he was not concerned by the results of either negative test.

Earlier today at the hearings:

At investigative hearings in Houston, questions were raised about whether firefighting efforts at the Deepwater Horizon after it exploded April 20 could have contributed to the sinking of the rig and the spilling of millions of barrels of oil.

Daun Winslow, a Transocean manager who was visiting the rig when it blew up, escaped the rig and stayed aboard the support vessel Max Chouest as it coordinated workboats that tried to fight the massive fire April 21.

Winslow said that sometime during the day after the explosions, his superiors in Houston told him to direct the response vessels to only shoot water at the rig's massive support columns. He said he had to repeatedly ask that the boats not shoot water onto the rig floor and derrick as the floating drilling unit listed badly.

But he said that none of the Coast Guard vessels coordinating the response ever contacted him about how the fire should be fought.

Winslow was directing a lot of the action during the firefighting, and he said "apparently" he was in charge until two contractors arrived to coordinate.

"We did not have a plan to put the fire out," Winslow said. "I do not believe the fire would be extinguished."

Winslow said he tried several times to use remotely operated vehicles -- unmanned submarines -- to execute a "hot stab," in which the underwater robots plug hydraulics on the blowout preventer on the sea floor to try to force it to close off the top of the well. Winslow said he was sent directions and schematics, but his e-mail couldn't handle the size of the computer files and he wasn't able to look at several of them.

The effort failed, as did many other attempts to activate the blowout preventer closures in the weeks and months ahead.

Some have suggested that if the rig had been allowed to burn or if the fire was simply contained, very little oil would have spilled from above and the vessel may not have sunk, in which case the mile-long riser pipe running down to the well might not have crumpled and leaked.

But comments posted on the Internet by eyewitnesses at sea in the hours immediately after the accident indicated that the rig was listing well before the fireboats were fighting the blaze at full force.

The rig crew tried unsuccessfully to disconnect the floating rig from the riser, which would have cut off the ignition source of the fire. In such a scenario, the oil would have continued to gush, but the riser may not have broken and it could have been significantly easier to cap it from the surface, rather than the 100-day-long, deep-sea saga that followed.